Underwater projectile

ABSTRACT

An efficient underwater projectile is disclosed having a frustoconical nose end, a long thin shank and a shroudless, stepped parallel side wall finned rear section with a forward facing abrupt shoulder formed thereon between two parallel longitudinal edge surfaces, the forward edge surface terminating at a sloped edge surface connecting with the shank, and the fins being joined at the shank body by a rearwardly tapered body section with triangular tapered and rearwardly inwardly sloping outer separation surfaces between the fins.

United States Patent [191 Monson et al.

[ Oct. 28, 1975 UNDERWATER PROJECTILE [75] Inventors: Franklin A.Monson, Glen Arm;

Kenneth E. Mueller, Baltimore City, both of Md.

[73] Assignee: AAI Corporation, Cockeysville, Md.

[22] Filed: July 16, 1971 [21] App]. No.: 163,476

Related U.S. Application Data [63] Continuation of Ser. No. 734,291,June 4, 1968,

abandoned.

[52] U.S. Cl l02/92.1; 102/48 [51] Int. Cl. F42B 11/00 [58] Field ofSearch 102/48, 92.1; 114/20 [56] References Cited UNITED STATES PATENTS3,434,425 3/1969 Critcher 114/20 Primary ExaminerSamuel FeinbergAssistant Examiner-C. T. Jordan Attorney, Agent, or FirmReginald F.Pippin, Jr.

[57] ABSTRACT An efficient underwater projectile is disclosed having afrustoconical nose end, a long thin shank and a shroudless, steppedparallel side wall finned rear section with a forward facing abruptshoulder formed thereon between two parallel longitudinal edge surfaces,the forward edge surface terminating at a sloped edge surface connectingwith the shank, and the fins being joined at the shank body by arearwardly tapered body section with triangular tapered and rearwardlyinwardly sloping outer separation surfaces between the fins.

14 Claims, 5 Drawing Figures US. Patent Oct. 28, 1975 3,915,092

I70 ll Franklin A. Monson Flg. 3 Kenneth E. Mueller INVENTOR ATTORNEYUNDERWATER PROJECTILE This is a continuation of Ser. No. 734,291 filedJune 4, 1968, now abandoned.

This invention relates to underwater projectiles, and particularly to animproved underwater projectile flechette type incorporating a particularconfiguration which maximizes velocity, range and target penetration,particularly in the range of depths of up to 90 feet and the underwatervisibility range at depths up to 30 feet.

In the prior art, various projectile arrangements have been employed forunderwater ammunition, the most common being spear gun projectiles andshot shell power heads, as well as combined shot shell and spearprojectiles. Such prior configurations have been substantially less thanfully effective, due to such deficiencies as cumbersome size, limitedvelocity, limited effective range and small terminal energy for targetpenetration.

It is an object and feature of this invention to provide an underwaterprojectile of superior velocity, range and target penetration in waterdepths of up to 90 feet and at ranges extending up to the effectivevisibility range at these depths.

Still other objects, features and attendant advantages will becomeapparent to one skilled in the art from a reading of the followingdetailed description of a single preferred embodiment constructedaccording to the invention, taken in conjunction with the accompanyingdrawings wherein:

FIGS. 1 and 2 are perspective views of a flechette projectile accordingto the invention.

FIG. 3 is fragmentary longitudinal side view of the rear sectionprojectile of FIGS. 1 and 2, showing its sta bilizing fin construction.

FIG. 4 is a rear end view of the underwater projectile of FIGS. 1 and 2.

FIG. 5 is a view of the projectile during manufacture, and showing thefins in full line prior to final formation, and the broken line in thefinal configuration of FIG. 3.

Referring now in detail to the Figures of the drawings, the projectile11 includes a cylindrical shaft or shank 13 having a frusto-conical nosesection 15 with a flat tip end 15a, and a stabilizing tail sectionincluding canted stabilizing fins 17 each having parallel opposite sidewalls 17k, 17k.

The overall length B of the fins 17 is approximately four shaftdiameters and the overall length A of the frusto-conical nose section 15is approximately three ,and one-half shaft diameters.

The four stabilizing radial fins 17 are integrally formed with the shank13, as by hot or cold metal working of the shank body to form thedesired configuration, as through the medium of a suitable forming die,

to an initial configuration as shown in full lines in FIG. 5, with thecurved outer edge 17f of the fins resulting from the amount of materialdisposed from the shank cylindrical blank into the fin formations whenthe die is pressed in to form the substantially flat or concavetriangular rearwardly and inwardly tapered connecting surfaces 17gbetween the fins 1 7t. Surface grinding of the radially outer surface ofthe fins is employed to effect the desired intermediate and rearwardradial surface final configuration as shown at l7a,'"l 7b," 170 axis ofthe shank 13. It will be appreciated that the canted fins 17 contributeto trajectory accuracy by imparting spin to the projectile, whereby fora given yaw angle the canted fin projectile dispersion is helical andhas a smaller radius of error dispersion than that which would beobtained by a straight finned configuration with a unidirectionaldispersion. The fins 17 are formed by the initial die forming step withan inclined forward face I7d. The intermediate forward reduced span ordiameter section having a ta dially outer surface 17a of substantiallyconstant diameter and the enlarged span or diameter rear section havingits radially outer surface 170 also of substantially constant span alongits length are initially die formed and then surface ground as discussedabove. At the longitudinal junction of reduced span section 17a andenlarged diameter rear section 170 of each fin is radially extendingforwardly facing flat surfaced shoulder 17b which is also formed bysurface grinding, preferably during the grinding of the radially outersurfaces 17a and 17c. The diameter of the larger diameter rear constantdiameter surface 17c substantially equal to approximately one andone-fourth to one and two-fifths diameters of the shaft or shank 13, andthe smaller diameter intermediate surface is approximately one andone-tenth to one and one-fifth shank diameters, the depth of theshoulder 17b being approximately onetenth to one-fifth shank diameters.

The cone angle of the frusto-conical nose section 15 is 10 (:I),included, and the flat tip end 15a of the frustum is approximately 0.30to 0.35 of the diameter of the shaft or shank 13.

The overall length of the projectile is equal to between 30 and 43 shaftdiameters, with a preferred length of 43 diameters for minimum desiredmuzzle velocity of approximately 700 to 750 feet per second andassociated launching propellant chamber pressures.

In one illustrative and preferred embodiment in which the shaft diameteris 0.100 inch, the shoulder has a depth of 0.010 inch, and the outerdiameter of the rear fin surface 17c is 0.131 inch. Also, in thisparticular preferred embodiment, the projectile shank 13 is formed oftungsten, the overall weight being grains, and the overall length being4.3 inches, with a frustrum cone angle of 10 and a tip diameter of 0.030inches.

In operation, the launching velocity of the projectile is preferablynear that of atmospheric pistol ammunition, being approximately 700 to750. feet per second, and whereas drag forces render atmospheric bulletshapes and other flechette shapes ineffective in very short ranges underwater, the present projectile is far superior in its range capabilityunder water. The high mass per frontal area and specific nose and tailproportions contribute mutually to an efficiently low coefficient ofdrag, and the stability of the projectile flight is also maximized bythe same balance of proportions.

Prior copending application Ser. No. 650,374 filed June 30, 1967, nowUS. Pat. No. 3,434,425, illustrates an ammunition arrangement throughthe medium of which similar, but shroudless shouldered finned underwaterprojectile is launched. A similar ammunition arrangement may be employedfor launching the shroudless, shouldered finned underwater projectileaccording to the present invention.

In operation, as the projectile flies through the water the flatfrustrum tip area 15a separates a bulk of water normal to thetrajectory, creating a cavitation envelope 3 of specific shape andlength relative to the instant projectile velocity and depth. Theinstantaneous cavitation envelope for velocities up to approximately 700feet per second and depths up to 90 feet has an effective lengthextending well back of the rear firmed section 17 of the projectile 11,and may be of a length up to several times the projectile length,dependent upon depth and instantvelocity before pressure can close thecavity. The cavity is difficult to precisely measure and define instructural contents; however, evidence indicates that the forward areaof the envelope surrounding the projectile body is composed of watervapor of varying density levels, the density gradient increasing at ahigh rate of change from the zone immediately adjacent the projectilebody to the zone at the edge of the cavitation envelope, and the linesof equal vapor density extend- I ing in something of an arcuate formfrom the zone of the flat tip a in a generally convex form along thelength of the projectile and the remainder of the envelope rearwardly tothe zone of closure where larger water droplets are forced into theenvelope zone. It has been found that the density gradient of the watervapor force from collision with the vapor within the cavitationenvelope, and as the water vapor thus exerts a drag force on thetailsection at the same time, it will be appreciated that the tailsection must be formed with the concept of minimizing contact with vaporwhile insuring sufficient stabilizing force to accomplish stability orprojectile flight. With the foregoing mentioned configuration andrelative dimensions and weights, for muzzle velocities of approximately700 feet per second and depths up to 90 feet, the projectile is nearlyfree of boundary layer drag forces over its effective range ex- .ceptfor the 'area of the frustrum flap tip end 15a, and the very minute dragforce exerted on the tail section 17 by the low density water vapor inthecentral zone of the. cavitation envelope cross section. The area ofthe flat tip end 15a is optimized for minimum drag and desiredcavitational envelope vapor impingement for stability control on thetail section 17, a frustrum tip end 15a of smaller proportion producingerratic flight with severe jaw resulting in negligible effective range,

' whereas increase in the proportions of the flat tip end 15a results inhigher drag forces at this zone, which also decreases the effectiverange. In addition, it has been found that increases in the cone angleof the nose section 15, and/or the outer diameter of the fins 17 alsoresults in higher drag forces which decrease the effective range, aswill be apparent from considerations of the rapid radial increase invapor density of the water vapor within the cavitation envelope. Whileuse of a shroud as disclosed in application Ser. No. 650,374 now U.S.Pat. No. 3,434,425, effectively minimizes yawing and increases flightaccuracy of the projectile theshroud also reduces velocity materiallymore than the present invention, particularly due to the inherentlylarger frontal and surface area of the shroud and the drag resultingfrom axially vectored impingement of the water vapor particles on thelarge frontal and outer surface area. The present intermediate shoulders17b betweenthe two constant diameter surfaces 17a, 17c von the fins 17have surprisingly been found to be sub 4 stantially equivalent inreducing and have resulted in further increased accuracy, apparently duelargely to the materially less drag, and higher terminal velocities orlonger effective range for a given initial velocity than that of theprior shrouded finned projectile. Further, while the shrouded projectileof U.S. Pat. No. 3,434,425 is quite satisfactory in shallow depths, thisshrouded projectile has inadvertently decreased accuracy as water depthincreases, and the present shroudless stepped shouldered finnedprojectile has been found .to afford materially better accuracy atincreased depthsthan the shrouded projectile, due to its decreased dragand higher terimal velocities at such depth, as compared to priorshrouded finned projectile.

It has further been found that reduction of the overall length relativeto diameter and tip end area results in less momentum withproportionate. loss in effective range, unless the launching velocity isincreased inversely proportionate to the length reduction. In thisrespect, the preferred length of the overall projectile 11 has beenfound to be 43 diameters, and by a sacrifice of higher launchingvelocities and associated higher chamber pressures the length of theprojectile has been successfully varied down to a length of 30 shaftdiameters. It will, of course, be appreciated that such requirement forhigher launching velocities and associated higher firing chamberpressures for launching the projectile put severe requirements upon theweight and strength of the launching ammunition arrangement and/orbarrel with consequent increase in bulkiness and the weight of theequipment and decrease in efficiency of power utilization.

It has been found that the terminal efficiency of the remaining energywhen the projectile is at a 30 foot range, which isthe generalvisibility range in shallow water of up to 3 foot depth, equals normallybetter than approximately one-half that of the energy of the projectileat the launch location, and produces penetration force concentration ofan extreme degree over a distance equal to and beyond this 30 footvisibility range. At the foot depth the terminal efficiency of theremaining energy is about 25% of that of the launch location energy ofthe projectile, with consequent lesser but effective penetration force.

It will accordingly be appreciated that the critical interrelation ofthe various parameters of the projectile are effective overall toprovide a highly desirable and useful underwater projectile which may beeffectively used by underwater fishermen, divers, etc., with goodresults within the operating ranges of visibility in water depths up to90 feet, and using launching velocities conventional to atmosphericpiston ammunition in the vicinity of 700 feet per second.

While the invention has been described with respect to a singleillustrative and preferred embodiment, it will be apparent to thoseskilled in the art that various modifications may be made withoutdeparting from the scope and spirit of the invention. Accordingly it isto be understood that the invention is not to be limited by theillustrative embodiment, but only by the scope of the appended Claims.

That which is claimed is:

1. An underwater projectilecomprising:

a long thin shaft having a cylindrical shank section, a frusto-conicalforward nose section, and a finned tail section,

said frusto-conical nose section having a blunt tip end with a diametersubstantially one-third of the shank diameter for forming adrag-reducing cavitation envelope longer than said projectile duringpassage of said projectile through water,

said tail section being shroudless and having a plurality of radial finsformed thereon,

each of said fins having effectively water-engageably exposed spacedapart discrete forward and rearward radially outer longitudinallyextending edge surfaces separated by a radially extending forwardlyfacing steeply inclined effectively water engageably exposed shoulderformed intermediate the length of each respective said fin, and therebyforming a forwardly and radially water-engageably exposed mid-lengthstep.

2. An underwater projectile according to claim 1,

said fins each having substantially smaller sloped surfaces forward andrearward of said shoulder and materially longer than the radial depth ofsaid shoulder.

3. An underwater projectile according to claim 2,

said smaller sloped surfaces being of substantially zero slope andconstant diameter, and said shoulder being substantially normal to theaxis of said projectile.

4. An underwater projectile according to claim 3,

and a forwardly radially inwardly sloping outer edge surface formedforward of the forwardmost end of said substantially constant diametersurface on each of said fins and connecting with said cylindrical shanksection.

5. An underwater projectile according to claim 4,

the angle of inclination of the conical surface of said conical nosesection being in the range of approximately 9l 1, and said blunt tip endbeing flat.

6. An underwater projectile according to claim 5,

said nose cone angle being substantially 10.

7. An underwater projectile according to claim 6,

said shaft having a length of between approximately 30 and 43 shankdiameters.

8. An underwater projectile according to claim 6,

said shaft having a length of substantially 43 shank diameters.

9. An underwater projectile according to claim 7,

said fins having a length of approximately four shank diameters,

said fins having their rearmost constant outer diameter equal toapproximately l-l/5 to l-2/5 shank diameters and their forwardmostconstant diameter surfaces equal to approximately l-l/lO to l-l/S shankdiameters.

10. An underwater projectile according to claim 7,

said fins having a rear diameter of approximately 1-1/3 shank diameters,with a shoulder depth of approximately l/lO shank diameter.

11. An underwater projectile according to claim 1,

each of said fins having a two-stepped radially outer edge surfaceextending parallel with the axis of said shaft, with said extending saidshoulder being contiguous with and connecting between said edge surfaceand extending normal to said shank axis.

12. An underwater projectile according to claim 11,

said fins being canted at an angle of approximately 2 to the shaft axis,

said shoulder being disposed approximately midway between the forwardand rear ends of said fins.

13. An underwater projectile according to claim 11,

said fins each having substantially planar parallel side wall surfaces.

14. An underwater projectile according to claim 13,

and interconnecting rearwardly and laterally inwardly tapered surfacesformed and connecting between said fins, the forwardmost end of saidtapered surfaces being forwardly arcuately convex.

1. An underwater projectile comprising: a long thin shaft having acylindrical shank section, a frustoconical forward nose section, and afinned tail section, said frusto-conical nose section having a blunt tipend with a diameter substantially one-third of the shank diameter forforming a drag-reducing cavitation envelope longer than said projectileduring passage of said projectile through water, said tail section beingshroudless and having a plurality of radial fins formed thereon, each ofsaid fins having effectively water-engageably exposed spaced apartdiscrete forward and rearward radially outer longitudinally extendingedge surfaces separated by a radially extending forwardly facing steeplyinclined effectively waterengageably exposed shoulder forMedintermediate the length of each respective said fin, and thereby forminga forwardly and radially water-engageably exposed mid-length step.
 2. Anunderwater projectile according to claim 1, said fins each havingsubstantially smaller sloped surfaces forward and rearward of saidshoulder and materially longer than the radial depth of said shoulder.3. An underwater projectile according to claim 2, said smaller slopedsurfaces being of substantially zero slope and constant diameter, andsaid shoulder being substantially normal to the axis of said projectile.4. An underwater projectile according to claim 3, and a forwardlyradially inwardly sloping outer edge surface formed forward of theforwardmost end of said substantially constant diameter surface on eachof said fins and connecting with said cylindrical shank section.
 5. Anunderwater projectile according to claim 4, the angle of inclination ofthe conical surface of said conical nose section being in the range ofapproximately 9*-11*, and said blunt tip end being flat.
 6. Anunderwater projectile according to claim 5, said nose cone angle beingsubstantially 10*.
 7. An underwater projectile according to claim 6,said shaft having a length of between approximately 30 and 43 shankdiameters.
 8. An underwater projectile according to claim 6, said shafthaving a length of substantially 43 shank diameters.
 9. An underwaterprojectile according to claim 7, said fins having a length ofapproximately four shank diameters, said fins having their rearmostconstant outer diameter equal to approximately 1-1/5 to 1-2/5 shankdiameters and their forwardmost constant diameter surfaces equal toapproximately 1-1/10 to 1-1/5 shank diameters.
 10. An underwaterprojectile according to claim 7, said fins having a rear diameter ofapproximately 1-1/3 shank diameters, with a shoulder depth ofapproximately 1/10 shank diameter.
 11. An underwater projectileaccording to claim 1, each of said fins having a two-stepped radiallyouter edge surface extending parallel with the axis of said shaft, withsaid extending said shoulder being contiguous with and connectingbetween said edge surface and extending normal to said shank axis. 12.An underwater projectile according to claim 11, said fins being cantedat an angle of approximately 2* to the shaft axis, said shoulder beingdisposed approximately midway between the forward and rear ends of saidfins.
 13. An underwater projectile according to claim 11, said fins eachhaving substantially planar parallel side wall surfaces.
 14. Anunderwater projectile according to claim 13, and interconnectingrearwardly and laterally inwardly tapered surfaces formed and connectingbetween said fins, the forwardmost end of said tapered surfaces beingforwardly arcuately convex.